1. Field of the Invention
The present invention relates to a vacuum chuck. In particular, the present invention relates to a vacuum chuck used in an exposure apparatus.
2. Description of the Related Art
During the fabrication of an LCD, an exposure process is performed for forming an electric circuit pattern on a flat glass panel used in the LCD. In general, the exposure process includes a first step in which a photoresist is coated onto the flat glass panel. The photoresist has a photosensitivity to light of a specific wavelength. The photoresist is then exposed to light after a reticle, on which an electric circuit pattern is formed, is placed on the coated, flat glass panel.
An exposure apparatus for an LCD, used in the above exposure process, comprises a reticle stage for loading a reticle on which a circuit pattern is formed. The apparatus also includes a movable plate stage for absorbing and fixing the flat glass panel. Lenses are then arranged between the reticle and movable plate stages in order to focus light received from an exposure light source. In addition, a device such as a blinder is installed in the flat glass panel for illuminating the light through the reticle.
In the above exposure apparatus, the plate stage has a vacuum chuck for holding the flat glass panel. The vacuum chuck keeps the flat glass panel level by holding it with a vacuum. In other words, the vacuum keeps the flat glass panel from moving even when the plate stage is moved.
FIG. 1 illustrates a prior art exposure apparatus. In the exposure apparatus 10 of FIG. 1, a plate stage 12 is arranged to be movable on a base 11. On the upper portion of the plate stage 12 is installed a vacuum chuck 13. The vacuum chuck 13, in turn, holds a flat glass panel 14 for an LCD onto its upper portion.
The operation of the vacuum chuck 13 will be described with reference to FIGS. 2a and b. width and length of the vacuum chuck 13 is represented in the drawings by m and n, respectively. On the upper surface of the vacuum chuck 13, a plurality of bearing portions 22 are formed. These bearing portions 22 project to a predetermined height from the upper surface of the vacuum chuck 13, and act to prevent the glass panel 14 from being deformed by its weight when it is placed on the vacuum chuck 13. A side wall 23, having the same height as that of the projecting bearing portion 22, is formed around the vacuum chuck 13. The vacuum chuck 13 also has a plurality of vacuum holes 21 which are connected to an external vacuum source (not shown).
When the flat glass panel 14 is put on the vacuum chuck 13 in FIG. 2a, a sealed space is formed between the upper surface of the vacuum chuck 13, the lower surface of the flat glass panel 14, and the side wall 23. Thus, a vacuum is formed when the air in the sealed space is sucked through the vacuum holes 21 by the vacuum source. The vacuum, therefore, will fix the flat glass panel 14 onto the vacuum chuck 13. The above vacuum is illustrated in FIG. 2b, and is formed in the space marked by reference numeral 24.
The prior art vacuum chuck described above, however, has some problems. The most basic of these is that the size of the flat glass panel 14, which may be fixed by the vacuum chuck 13, is limited. In other words, the width and the length of the flat glass panel 14 must be the same as the width m and length n of the vacuum chuck 13. If the flat glass panel 14 is larger or smaller than the vacuum chuck 13, a vacuum cannot be formed in the space 24, and, therefore, the glass panel 14 cannot be fixed to the vacuum chuck 13. Thus, if the size of the flat glass panel 14 is changed (i.e., due to a consumer request, a change in plans, etc.), then the entire stage must be re-designed. Furthermore, even if the vacuum chuck 13 is the only part which needs to be changed, productivity will decrease and expenses will increase since much time is spent re-setting the exposure apparatus 10.
Therefore, it is an object of the present invention to provide a vacuum chuck which can hold differently sized parts through the use of a vacuum. Another object of the present invention is to provide a vacuum chuck having a plurality of compartments in which a vacuum can be independently formed in each compartment. It is still another object of the present invention to provide a vacuum chuck which can automatically control which compartments will have a vacuum and which will not.